DESCRIPTION: (Applicant's Abstract): Dyscoordination of the proximal arm is a malady that can result from several types of diseases including stroke, cerebellar ataxia, and disorders of the basal ganglia. Despite progress in understanding the cellular and genetic basis of these diseases, research gains at the systems level are few, perhaps due to the neural and mechanical complexity of movement disorders. The unique contribution of the proposed work is that it bridges the gap between neuroscience and biomechanics. The proposed experiments will reveal how musculoskeletal constraints dictate optimal neural control strategies. Specific aim 1 is to test the hypothesis that an optimization of movement dynamics governs the neural control of natural reaching movements. Three experiments involve an analysis of reaching from various initial locations to various target location, coupled with calculations of optimal force-control strategies. Specific aim 2 is to improve our understanding of the relation between muscle activation and joint torque. Studies of the neural control of reaching have been impeded by a lack of understanding of musculoskeletal mechanics. This problem will be solved by obtaining additional information of muscle mechanics and constructing a model of sufficient detail to test hypothetical neural control strategies. the long-term objective of this work is to understand the complex neuromuscular pattern, produced so naturally by the central nervous system, during daily reaching movements. The issues examined by this basic research are relevant to efforts in rehabilitation from limb paralysis.